Diverse actin structures drive the ability of cells to polarize, crawl, communicate and divide. The assembly of many of these actin structures depends on the actin nucleating proteins, the formins. A key question is how formins are positioned and regulated to build actin structures at specific sites on the cell surface at the right times. We study cell polarization and cytokinesis in fission yeast Schizosaccharomyces pombe, and focus on the regulation and function of formins. Microtubules regulate the formin forSp and actin cable assembly for cell polarization, through microtubule plus end proteins teal p and tea4p. The nucleus regulates the positioning of the cytokinesis formin cdc12p and the actin contractile ring through a nuclear shuttling protein mid1p. In addition to just actin assembly, our preliminary results suggest that formins have key regulatory functions in initiating cell polarization and cytokinesis. Our specific aims focus on the dissecting that the molecular links and regulatory networks underlying these fundamental processes. Cell division and polarization are universal, cellular processes that serve as the basis for cellular function and proliferation. Mistakes, for instance, in cytokinesis are likely to contribute to the development of the cancer cell. These studies using fission yeast as a model organism are highly relevant towards understanding human cell biology and disease. [unreadable] [unreadable] [unreadable]